They have a lot of applications, so use them for a good amount of your PL goals.
Use them for hammering your posterior chain and for speed work.
If you have issues going well below parallel raw then it's a good way to gradually increase your strength lower and lower in the hole.
I really like them for adductor work and using them for wide squats to really stress the hips, similarly to deficit deadlifts.
Regarding box height- I'm only 5'9" but I've used as low as 8" for speed work.
I know StormTheBeach uses a 13" box and he's around your height, fwiw